The invention concerns a composition for a high-resolution photosensitive composition which can be developed by plasma, comprising a polymer and a photosensitive compounds, where the polymer is an acrylate and the photosensitive compound is an aromatic azide.
The invention is useful in the plasma-production of designs smaller than a micron in size with a photosensitive resin coating after the local irradiation of the photosensitive composition by electromagnetic radiation or a particle beam in order to form masks used at various stages in the manufacture of high-density integrated micro-circuits.
The invention also concerns the method of obtaining the photosensitive composition and the photolithographic process making use of it.
A photosensitive composition like the one described in the preamble is known from U.S. Pat. No. 4,401,745. This document describes a family of resins formed of a polymer and a photosensitive compound in which the polymer is a acrylic or vinyl ketone polymer with molecular weights of between 10.sup.4 and 2.times.10.sup.6 and where the photosensitive compound an aromatic azide. This patent also mentions the possibility of adding a third constituent in the form of a vinyl compound.
The photosensitive compositions described in the cited patent are of the negative type, i.e. the developing agent preferentially acts upon the non-irradiated parts.
These resins are used in the following manner:
After deposition on a substrate, the photosensitive compositions selected from the aforementioned group is locally irradiated in a predetermined pattern using ultra-violet or X-rays or an electron beam. It is then dry-developed using a plasma including oxygen, CF.sub.4, a mixture of the two or an oxygen-argon mixture. These plasmas preferentially act upon the non-irradiated parts, and local apertures are formed in the resin coating. The masks thus constituted are used in photolithography in the processes of making integrated circuits.
Nowadays, the size of microcircuit components is of the order of a micrometer (.mu.m) or even smaller. Therefore, the patterns formed in the resins used in photolithography must be of the same order of magnitude. The qualities of the photosensitive composition must thus be the best possible, especially with regard to resolution, sensitivity and selectivity.
By resolution is meant the minimum size of the patterns to be defined using the resin; by sensitivity, the minimum radiation dose needed to obtain a chemical change in the resin sufficient for development; and by selectivity, the difference between the rates at which the irradiated and non-irradiated areas are affected.
Photolithographic processes including the use of dry-developed compositions, i.e. by plasma, like the known from the cited document, have many advantages over those in which the compositions are wet-developed, i.e. in a developer bath. In particular, they make it possible to treat numerous samples with better reproducibility. Moreover, they facilitate the integration of the resin development stage in a complete cycle for the manufacture of microcircuit components in vacuo. In addition, it is possible to produce the best possible contrast by improving the anisotropy of engraving by judicious control of the plasma parameters. Finally, they make it possible to take advantage of good sensitivity, an inherent property of negative photosensitive compositions, without limiting the resolution, which happens when negative photosensitive compositions resins are wet-developed, where the loss of resolution is caused by a "swelling" phenomenon ascribable to the developer.